JP2001321985A - Gas shielded arc welding wire for thin steel sheet and pulse mag welding method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas shielded arc welding wire which is good in the crosslinkability in a gap of a large clearance of welding materials, prevents the weld crack liable to occur during solidification of weld metal, is excellent in the removability of weld slag and decreases spatters in gas shielded arc welding of thin steel sheets and a pulse MAG welding method using the same. SOLUTION: This gas shielded arc welding wire for the thin steel sheets contains, by mass % 0.03 to 0.20% C, 0.5 to 2.0% Si, 0.8 to 3.0% Mn, <=0.015% P, <=0.005 S, 0.005 to 0.0300% O, further contains 0.005 to 0.200% total of one or total of >=2 kinds among La, Ce, Zr and Ti and 0.005 to 0.200% one or total of >=2 kinds among Bi, Sb, As, Pb, and Sn, and consists of the balance Fe and inevitable impurities.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas shielded arc welding of a thin steel plate, which has good crosslinkability in a large gap between welding members and prevents welding cracks which are likely to be generated at the time of solidification of a weld metal. TECHNICAL FIELD The present invention relates to a gas shielded arc welding wire having excellent slag peelability and less spatter, and a pulse MAG welding method using the same.

[0002]

2. Description of the Related Art Conventionally, in the welding of a thin steel plate such as a welded structure or an automobile, a machine, or an electric part, automation by a welding robot is frequently used for the purpose of improving productivity, and the welding speed is 1 m.
/ Min or more in many cases.

[0003] Further, since members are becoming thinner in order to reduce the weight, measures such as burn-through are required in arc welding, so that the welding current must be set lower. However, it is difficult to stably form a good weld bead because the welding conditions must be considered from the viewpoint of ensuring the penetration.

[0004] Further, in welding members such as automobiles, the so-called gaps between members tend to increase due to complicated joint shapes. In such a situation, the range of good welding conditions for satisfying the bridging property with respect to the gap of the member to be welded is also narrowed, so that it is required to perform stable welding with satisfactory burn-through resistance as well as gap resistance. I have.

[0005] In recent years, high-P steel materials with an increased P have been developed and put into practical use in automobile parts and the like in order to increase corrosion resistance. When this P-added thin plate is welded,
In some cases, a low melting point alloy of P in the weld metal and other weld metal components was formed, and high-temperature cracking was likely to occur and a healthy weld was not obtained. Further, there are many weldings using a combination of a high P steel material and a normal steel plate, and crack resistance is often a problem.

[0006] Even in the case of ordinary steel plates, particularly when a thin steel plate or a steel pipe is subjected to gas shielded arc welding, the heat input per unit thickness becomes excessively large as compared with a thick plate, and the deformation of the welded portion becomes large. Therefore, the risk of cracking of the weld metal has increased. Furthermore, when the gap between the members is large, the influence of solidification shrinkage of the weld metal is large, and the occurrence of cracks in the weld metal is a serious problem.

[0007] When a good weld bead is obtained, the member to be welded is usually coated as a whole after welding and assembling, but the slag is formed, and the slag adhered portion cannot be coated. In addition, there has been a problem that the slag is peeled off after a lapse of time, the corrosion property and the like are significantly deteriorated due to the exposure of the weld metal surface, and the appearance becomes poor. Furthermore, not only does the accuracy of the welded member deteriorate due to an increase in the amount of spatter generated, but it is also a major factor in cost increase due to spatter removal and the like.

As a countermeasure against these problems, automation using a welding robot by pulse arc welding has been advanced. However, the above problems tend to be more obvious as a factor inhibiting the automation, and it is strongly desired to solve these problems. It is rare.

Regarding MAG welding for thin high-tensile steel, Japanese Unexamined Patent Publication No. 7-195193 states that if there is a non-uniform strength distribution between the base metal and the weld metal, there is a risk that weld cracks will occur. . Therefore, a solid wire for high-tensile steel has been proposed in which the difference in strength between the base metal and the weld metal is made small, the strength is balanced, and crack resistance is taken into consideration, and the wire cost is reduced. However, the crosslinkability aimed at by the present invention has not been improved, and
No consideration is given to the slag removability. Furthermore, Japanese Patent Application Laid-Open No. H8-243749 proposes a pulse MAG welding method that prevents burn-through and enables high-efficiency welding, but does not improve the peelability of welding slag and the like.

[0010]

DISCLOSURE OF THE INVENTION In view of the above-mentioned problems of the prior art, the present invention has good crosslinkability in gas shielded arc welding of a thin steel plate even in welding with a large gap between members to be joined. It is an object of the present invention to provide a gas shielded arc welding wire which prevents welding cracks generated at the time of solidification of a weld metal, has excellent peelability of welding slag, and generates little spatter, and a pulse MAG welding method using the same.

[0011]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, that is, the gist thereof is as follows. (1) In mass%, C: 0.03 to 0.20%, Si:
0.5-2.0%, Mn: 0.8-3.0%, P: 0.
015% or less, S: 0.005% or less, O: 0.005
0 to 0.0300%, and La, Ce, Z
0.005 in total of one or more of r and Ti
0.005 to 0.200% in total of one or more of Bi, Sb, As, Pb and Sn
And a balance consisting of Fe and inevitable impurities. (2) The gas-shielded arc welding wire for thin steel sheets described in (1) is used, and Ar gas and C are used as shielding gases.
O ₂ gas mixed gas or Ar gas, the pulse MAG welding wherein the welding by using a mixed gas of CO ₂ gas and O ₂ gas. (3) Further, the peak current of the pulse current: Ip = 380
６680 A, pulse peak time: Tp = 0.6２2.8.
The pulse MAG welding method according to (2), wherein msec, base current: Ib = 20 to 100 A.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In gas shielded arc welding of a thin steel plate, the present inventors have made it possible to improve the cross-linkability during welding in a gap having a large gap between members to be welded, and to improve the welding generated when the weld metal solidifies. The goal is to prevent the occurrence of high-temperature cracking due to S, which is the element that forms low-melting sulfides, when welding high P-added steel sheets with increased P in order to prevent cracking and ensure corrosion resistance. I made it. For this reason, it was decided to suppress the hot cracking by lowering the S content of the wire. Further, sulfide-forming elements La, Ce,
It was considered effective to fix S in the molten metal by Zr and Ti and to suppress the occurrence of hot cracking.

Further, Bi, Sb, As, Pb and Sn act as surface active elements on the surface tension of the welding slag, and the addition of these increases the difference in interfacial tension with the welding metal. There is an effect that the shape becomes scattered on the bead surface and the peelability of the weld slag after solidification is excellent.

From this point of view, studies were made on the optimization of the wire composition and the shielding gas composition and on the selection of the pulse conditions, and the configuration of the present invention was assured. Hereinafter, the present invention will be described in detail. First, the reasons for limiting the components of the wire of the present invention will be described.

C is an element that secures the strength of the weld metal. However, if C is added in excess of 0.20%, the primary crystal during solidification becomes an austenite (γ) phase, and hot cracking is likely to occur. This has a great effect on the hot cracking of the weld metal during welding of P-added thin steel sheets and the like. Further, when the content of C is kept low, the short-circuiting property of the molten metal during arc welding tends to decrease, and the arc state is likely to be unstable. Is 0.03
% Is required.

Although Si is added as a deoxidizing agent, it is also an element that induces high-temperature cracking, and it is preferable that the content be small. However, if it is less than 0.5%, the gap resistance cannot be ensured, so the lower limit is 0.5%.
And On the other hand, if it exceeds 2.0%, the crack resistance deteriorates.

Mn is also added as a deoxidizing agent like Si, but in gas shielded arc welding, if it is less than 0.8%, deoxidation becomes insufficient and a sound weld bead cannot be formed. In addition, S, which is a welding crack inducing element, has the effect of forming a compound of MnS and improving crack resistance.
% Or more can obtain the effect. On the other hand, if it exceeds 3.0%, the strength of the weld metal is increased and the crack resistance is poor, and the workability is deteriorated due to an increase in the amount of slag and the like. Furthermore, since the strength increases at the stage of processing into a wire, the drawability deteriorates, so the upper limit was set to 3.0%.

P is an element that inhibits cracking resistance and forms a compound having a low melting point, such as Fe ₃ P, and deteriorates cracking resistance. In particular, in the wire of the present invention to which a large amount of Si or Mn is added, it is preferable to suppress as much as possible.
If it is 5% or less, the purpose is achieved. In particular, for a steel sheet containing a large amount of P to improve corrosion resistance, the amount of P in the welding wire must be kept low and the amount of P in the weld metal must be considered.

S forms a compound having a low melting point such as FeS, and when segregated, cracks are induced at the solidification stage of the weld metal. In the case of gas-shielded arc welding of thin steel plates and steel pipes even for ordinary steel plates, the welding heat input per unit thickness becomes excessive and the deformation of the welded parts becomes large compared to thick plates. Further, when the gap between the members is large, the influence of the solidification shrinkage of the weld metal is large, and the occurrence of cracks in the weld metal due to segregation of S becomes remarkable. In a steel sheet in which a large amount of P is added to improve the corrosion resistance, the cracking property of the weld metal is particularly remarkable, so that it is necessary to keep it low, and the addition amount is 0.005% or less.

La, Ce, Zr and Ti are sulfide-forming elements and form sulfides such as La ₂ S ₃ , CeS, ZrS and TiS. These sulfides are stable and have a freezing point of Fe
S can be removed or fixed higher than the above, and cracks due to S can be reduced. La, Ce, Zr, and Ti are effective at 0.005% or more in total of one type or two or more types.
If it exceeds 0.200%, stable bead transfer characteristics during welding are inferior, and the arc becomes unstable, so that good beads cannot be formed.

Bi, Sb, As, Pb and Sn act as surface active elements on the surface tension of the welding slag, and when added, the difference in interfacial tension with the welding metal becomes large,
It has the characteristic of making it difficult to cover the slag uniformly, and has the effect of excelling in the peelability of the welding slag. Further, since the uniformity of the bead crests is obtained, the bead appearance and shape are improved. The effect is recognized at 0.005% or more in total of one or two or more kinds. However, if the content is too large, the detachment of the droplet is bad and irregular, the arc state is deteriorated, and the occurrence of spatter and crosslinkability cannot be secured. Therefore, the upper limit is 0.200
%.

O stabilizes the arc, reduces the amount of spatter generated, smoothes the bead, secures the bead width, and has the effect of improving the crosslinkability. O is required to be 0.005% or more. It becomes longer, lowering the arc stability and spattering frequently. In addition, there is a disadvantage that the amount of slag generated on the bead surface is increased and the slag encapsulation rate is further increased. However, coexistence with S reduces the slag-encapsulated area and exerts a function of improving the releasability. This effect is small when the O content exceeds 0.0300% in the range of the S content of the present invention.

N is preferably as small as possible from the viewpoint of ensuring toughness, and not only causes blowholes but also spatters. Particularly, when it exceeds 0.008%, spatters increase remarkably. In addition, as a result of varying the arc length when spatter occurs, the stability of the arc is significantly reduced. Therefore, the content is preferably set to 0.008% or less.

Next, a method of pulse MAG welding using the above-described welding wire of the present invention will be described. In the present invention, by using a welding wire containing the above components and using a mixed gas of Ar gas and CO ₂ gas as a shielding gas, a stable arc state and low spatter welding can be achieved even in high-speed welding of thin steel sheets. It becomes possible. At this time, the mixing ratio of the CO ₂ gas in the shielding gas is 5 to 40 v
ol% is preferred. It is preferable to use a mixed gas in which an O ₂ gas is further mixed with an Ar gas and a CO ₂ gas as a shielding gas since a better penetration depth and bead width can be secured. At this time, the mixing ratio of O ₂ gas is
Less than 7 vol% is preferred.

Further, according to the present invention, the pulse MA
When performing G welding, the welding current is defined as follows. Pulse peak current: Ip = 380-680 A If the pulse peak current is less than 380 A, the detachment of the droplet by the electromagnetic pinch effect is not performed smoothly, and
If it exceeds 0 A, the transfer of droplets becomes irregular, and the amount of spatter increases. In addition, the arc length is increased, and welding defects such as undercut are liable to occur. Therefore, the pulse peak current is defined as Ip = 380-680A.

Pulse peak time: Tp = 0.6 to 2.8
msec When the pulse peak time is less than 0.6 msec, the energy for forming the droplet is insufficient, and when it exceeds 2.8 msec, the droplet grows excessively, and it is difficult to generate spatter frequently and secure a good weld bead. This causes a decrease in crosslinkability. Therefore, the pulse peak time is defined as Tp =
It is regulated to 0.6 to 2.8 msec.

Base current: Ib = 20 to 100 A The base current is a condition for maintaining the arc during the base period and ensuring arc stability. Base current is 2
If it is less than 0 A, the arc becomes unstable, and if it exceeds 100 A, the droplets are not rapidly separated, so that spattering frequently occurs and crosslinkability due to poor bead shape is also reduced. Therefore,
The base current is defined as Ib = 20 to 100A.

By applying the present invention, in gas shielded arc welding of a thin steel sheet, the bridging property is good in a gap having a large gap between welding members, and welding cracks which are easily generated at the time of solidification of a weld metal are prevented. In addition, gas shielded arc welding with less spatter can be performed, and a weld metal having excellent bead appearance and good bead appearance can be obtained, so that the welded portion is sufficiently satisfactory for a structure.

[0029]

EXAMPLES The effects of the present invention will be specifically described below with reference to examples. First, for the gap resistance, a wire shown in Table 1 was used and a SPCC polished steel plate shown in Table 2 was used, and a downward butt joint shown in FIG. 1 was used to form a taper gap having a gap of 2 mm to 4 mm. Under the welding conditions shown in Table 4, the gap at a position from the start of welding at a gap of 2 mm until the bridging of the weld metal disappears was determined as a weldable gap, and the width was measured. did. Further, the slag peelability was determined to be good when the slag generated in the weld bead evaluated for the gap resistance was lightly rubbed with a rag to peel. Further, in the evaluation of weldability, the arc stability and the degree of generation of spatter were visually judged, and the stability of welding and the like were evaluated. Table 3 shows the results.

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

[Table 3]

[0033]

[Table 4]

The P-added thin steel plate shown in Table 2 was used for the thickness 2.3 mm, the width 40 mm, and the length 330 mm using wires (diameter 1.2 mm) of the chemical components shown in Table 1 and shown in Table 4 below. After the test bead was welded on the plate by the test method as shown in FIG. 3 (a), as shown in FIG. 3 (b), the excess of the bead was removed, and a valestrain weld crack test piece was prepared.

A valley strain welding crack test by TIG welding, which is a bead vertical bending test, was performed on the upper surface of the test piece from which the excess was removed by the method shown in FIG. In addition, 1 in FIG. 2 is a P-added steel plate from which a surplus has been removed, 2 indicates a base block, a bending radius is 62.5 mm, a distortion amount is 1.84%, 3 is a test piece holding jig, and 6 is a ram. The descent position is shown. This ram descent speed is 500m
m / sec, 4 indicates a TIG test start position, and 5 indicates a TIG welding end position. After the balestrain welding crack test, the total length of cracks generated on the bead surface near the crater as shown in FIG. 4 was measured and evaluated with a high-power microscope up to 500 times, and the result of the total crack length was evaluated. As shown in Table 3 and Table 5, the total of the lengths of the weld cracks was less than 0.5 mm, which was regarded as acceptable. 4 is a P-added steel plate, 7 is a test bead, 8 is a TIG welding bead, 9 is a crater portion of the TIG welding, and 10 is a weld crack that has been cracked by a valestrain welding crack test.

[0036]

[Table 5]

Further, gas shielded arc welding was performed by changing the shield gas composition, pulse peak current, pulse peak time, and base current shown in Table 5. In addition to the weldable gap to the member gap at that time, the weld cracking property, the degree of slag adhesion and the releasability, it was confirmed whether stable welding and a good weld bead could be obtained.
Are also shown.

In Table 1, wire symbols A to J
Is a wire of the present invention, wherein C is 0.03 to 0.20% and S is
i is 0.5 to 2.0%, Mn is 0.8 to 3.0%, P is 0.015% or less, S is 0.005% or less, and O is 0.0
0.50-0.0300%, La, Ce, Zr, Ti
0.005 to 0.2 in total of one or two or more
It is in the range of 00%. Bi, Sb, As, Pb,
0.005 or more in total of one or more of Sn
It is in the range of 0.200%. Further, a wire symbol K to a wire symbol R indicate comparison wires.

Table 3 shows the results of the evaluation of the weldable gap, weld crack length, slag peelability, and weldability of these wire symbols A to R. With the wires of the present invention having the wire symbols A to J, a sound weld metal having a good weldable gap, less occurrence of high-temperature cracking by a balstrain welding crack test, good slag peelability welding, and good bead appearance can be obtained. Have been obtained.

On the other hand, for the wire symbol L in which the amounts of P and S of the wire are more than the range of the present invention, high-temperature cracking occurs frequently, and for the symbol M, since the C amount exceeds the range of the present invention, the occurrence of cracks increases. ing. The symbol N whose Si content is equal to or less than the present invention
Has a poor bead width because the bead width is small.

Further, since the symbol O has a small amount of C and Si, the arc state becomes unstable and the gap resistance cannot be ensured. The symbol K is an excess of La, Ce, Zr, and Ti added to improve crack resistance.
Bi, S added for the purpose of improving slag removability
Since b, As, Pb, and Sn were excessive, the amount of slag generated increased and the short-circuit transfer characteristics deteriorated, and the weldability tended to be significantly inferior. Therefore, the balestrain weld crack test was omitted.

In addition, La and Ce are added to the wire symbol R, but since the sum of the added amounts is less than 0.005%, the crack resistance is inferior. B for the purpose of improving slag removability
The wire symbol Q to which i and Sb were added had poor slag removability because the addition amount was less than 0.005%. The wire symbol P having an Mn content exceeding the range of the present invention also increased the amount of slag generated and deteriorated the short-circuit transfer characteristics, resulting in poor weldability, and further, the bead was cracked and the bead appearance was poor.

In Table 5, test symbols 19 to 24
Denotes a mixture of Ar having a shielding gas composition with an appropriate amount of CO ₂ or an appropriate amount of O ₂ gas. Symbols 28 to 31 indicate peak currents of pulse conditions: Ip of 380 A to 680 A, and peak time: Tp of 0.4 msec to 3. This is the method of the present invention performed under the conditions of 0 msec and a base current: Pb of 20 to 100 A. In these, the bead width was widened and the weldable gap was large due to the stability of the arc, the crosslinkability was good, there was no welding crack, and welding with good slag peelability was possible.

However, in test symbols 25 to 27, since the shielding gas contains a large amount of the CO ₂ gas and the O ₂ gas in the Ar gas, the arc becomes unstable, the spatter is large, and the bead forming property is inferior.

In addition, the symbols 32 to 35 were inadequate in pulse waveform conditions and could not perform good pulse welding, so that the weldability was poor and the bead shape was not uniform, so that the slag peelability was also deteriorated.

As described above, the application of the wire and the shielding gas of the present invention, and the selection of the pulse conditions, provide good cross-linkability in a large gap between the welding members in gas shielded arc welding of a thin steel plate, and the welding metal is not welded. Prevents welding cracks that easily occur during solidification. Further, it is apparent that gas shielded arc welding with less spatter can be performed, and that a weld metal having good peelability of weld slag and excellent bead appearance can be obtained.

[0047]

As described above, in the gas shielded arc welding of a thin steel sheet, the cross-linkability in a large gap of a welding member is good by the selection of the composition of the wire, the shielding gas, and the pulse conditions as described above. Prevents welding cracks that easily occur. Further, gas shielded arc welding with less spatter can be performed, and a weld metal having good peelability of welding slag and excellent bead appearance can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a steel plate and a welding gap of a material to be welded used in an example of the present invention.

FIG. 2 is an explanatory diagram of a balestrain welding crack test.

FIG. 3 shows (a) a cross section of a weld bead according to an embodiment of the present invention;
(B) It is a figure which shows the cross section which cut this extra bank.

FIG. 4 is a view showing a state of a weld bead of a test piece after a varestrain weld crack test.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Ryuichi Shimura 20-1 Shintomi, Futtsu City, Chiba Prefecture Nippon Steel Corporation Technology Development Division (72) Inventor Hatshiko Oikawa 20-1 Shintomi, Futtsu City, Chiba Prefecture New Japan F-term in Technical Development Division of Steel Corporation (reference) 4E001 AA03 BB06 CA07 DD02 DD04 DD05 DE04 EA05 EA08 EA10

Claims (3)

[Claims] C: 0.03 to 0.20%; Si: 0.5 to 2.0%; Mn: 0.8 to 3.0%; P: 0.015% or less; S: 0.005% or less, O: 0.0050 to 0.0300%, and further, 0.005 to 0.200% in total of one or more of La, Ce, Zr and Ti, Bi , Sb, As, Pb, Sn, one or two or more of them in a total content of 0.005 to 0.200%, with the balance being Fe and unavoidable impurities, gas shielded arc welding for thin steel sheets. Wire. 2. A gas-shielded arc welding wire for a thin steel sheet according to claim 1, wherein a mixed gas of Ar gas and CO ₂ gas, or Ar gas, CO
A pulse MAG welding method characterized by performing welding using a mixed gas of _two gases and O ₂ gas. 3. The pulse current peak current: Ip
= 380-680A, pulse peak time: Tp = 0.4
To 3.0 msec, base current: Ib = 20 to 100 A
The pulse MAG according to claim 2, wherein
Welding method.